1. Field of the Invention
The present invention relates to a tracking servo apparatus for use in a disk player.
2. Description of the Related Art
In a disk player for playing back an information record disk (hereinafter, simply referred to as "disk") such as a video disk and a digital audio disk, a tracking servo apparatus is indispensable for controlling the information reading spot of a pickup to accurately follow the record track at all times regardless of eccentricity of the disk or the like.
The tracking servo apparatus achieves the position control of the information reading spot relative to the record track by generating a tracking error signal corresponding to the amount of deviation of the information reading spot with respect to the record track of the disk in the radial direction of the disk and driving an actuator for shifting the information reading spot in the radial direction of the disk in in accordance with the tracking error signal, thus operating as a so-called closed loop controlling system. Further, such a servo apparatus, when making a so-called jump operation to allow the information reading spot to skip over some record tracks, performs controlling operations to apply an accelerating pulse to the actuator with the servo loop brought into an open state and then, at predetermined timing in the jump operation, apply a decelerating pulse to the actuator, and thereafter, at suitable timing, to execute a servo pull-in operation with the servo loop closed.
In the track jump control, since the track pitch of the disk is fixed by standards, the pulse width and pulse height of the accelerating pulse and decelerating pulse are set in accordance with the track pitch. There are, however, some nonstandard disks whose track has a large swell. At the time of playback of such a disk, if a track jump is performed at a portion of the track where it has a large deformation, the braking force produced by the decelerating pulse becomes smaller than the optimum value making it difficult for the servo apparatus to pull the information reading spot onto the target track, whereby overshoot is produced in the tracking error. Once the overshoot occurs, not only the jumping operation becomes unstable but also a continuing oscillation is produced in the subsequent playback.